AFAIK this code is not a valid c++ code by standard:
int a = 5;
int b[a];
but it seems many compilers can compile that code (mostly with warning) and it just behaves as expected. Am I wrong is is it compilers being nice to me?
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exact duplicate: [Dynamic array In Stack](http://stackoverflow.com/questions/1204521/dynamic-array-in-stack), [c++ initialize array with declared size as a value of an integer](http://stackoverflow.com/questions/6330695/c-initialize-array-with-declared-size-as-a-value-of-an-integer), ... – moooeeeep Nov 23 '11 at 08:24
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@fmaas: didn't find those questions sorry – Ali1S232 Nov 23 '11 at 08:45
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Actually I was aware of them just because I stumbled on this a few days ago by pure coincidence... – moooeeeep Nov 23 '11 at 09:03
3 Answers
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It is called variable length array (VLA) which is not allowed by Standard C++, any version of C++, though some GCC supports this as an extension.
If you're using GCC, then
- Compile it with
-pedanticoption, you will see warning. - Compile it with
-pedantic -Werroroption, you will see warning turned into error.
VLA is allowed only by C99, though not by other versions of C.
Nawaz
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Won't `-std=c++98` (or `-std=c++0x` if you're experimenting, rather than writing production code) suffice to suppress support of VLAs in g++? – James Kanze Nov 23 '11 at 08:38
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@JamesKanze: No. It doesn't. I tried with `-std=c++98`, `-std=c++03`, and `-std=c++0x`, but none of them suppresses VLA in g++. It is weird, though. I'm using MinGw version 4.6.1 :-) – Nawaz Nov 23 '11 at 08:42
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That sort of surprises me. But I'll admit that I've never tried it. (I always compile with `-std=c++98 -pedantic`. And in C++, I don't use `T[]` very often, either.) – James Kanze Nov 23 '11 at 09:10
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The compiler is being nice. :)
It's actually part of the C standard, and some compilers (like GCC) extend C++ with this feature.
Some programmer dude
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